Adjustable slotted wave guide radiator with coupling element



March 30, 1965 J. A. KUECKEN 3,176,300

ADJUSTABLE SLOTTED WAVE GUIDE RADIATOR WITH COUPLING ELEMENT Filed Jan.24, 1964 2 Sheets-Sheet l INVENTOR.

J OHN A. KUECKEN.

"MM M gmfiw 7 1. 7 701 ATTORNEYS.

March 30, 1965 J. A. KUECKEN 3,176,300

ADJUSTABLE SLOTTED WAVE GUIDE RADIATOR WITH COUPLING ELEMENT Filed Jan.24, 1964 2 Sheets-Sheet 2 INVENTOR.

JOHN A. KUECKEN 3,17 6,304 ADJUSTABLE SLOTTED WAVE GUIDE RADIATOR WITHCGUPLENG ELEMENT John A. Kuecken, Cincinnati, Ohio, assignor to AvcoCorporation, Cincinnati, Ohio, a corporation of Delaware Filed Jan. 24,1964, Ser. No. 340,914 3 Claims. (Cl. 343-767) This application is acontinuation-in-part of U.S. application Serial No. 91,168, filedFebruary 23, 1961, now abandoned.

The present invention relates to wave guides for use in ultra-highfrequency techniques, and specifically to a novel and readily adjustablewave guide radiator or slot antenna.

A primary object of the invention is to provide a radiator including acoupling element which is adjustable over a wire range of electricaladmittances.

Another object is to provide a radiator which is not so subject tocross-polarization problems as conventional radiators.

A further object of the invention is to provide a radiator which isreadily mechanically adjustable. This feature is of particular worth inwave guide arrays involving a plurality of slot-type radiators, theentire array being conventionally subject to radical impairment of itsdesired characteristics in the event of misalignment of one or more ofthe slots.

An ancillary object is to reduce the close tolerances and criticalcharacter normally required in slot antenna fabri cation.

Another important object of the invention is to provide the combinationof a rectangular wave guide formed with a normally substantiallynon-radiating slot extending parallel to the electric field and acrossthe short side of the guide, and a trombone-shaped, substantiallyinductive coupling element mechanically positioned obliquely to bridgethe slot and to provide a slot looped by the magnetic field.

A related object of the invention is to provide a radiator including aplurality of such slots and coupling elements.

A further object of the invention is to provide such a combination inwhich the coupling element is adjustable both as to angularity relativeto the slot and penetration of the wave guide.

The use of slotted rectangular wave guides in microwave transmission andreception would be materially enhanced if simple means were availablefor adjusting the coupling and radiation properties. The need for apractical solution of this problem led me to the concept of a combinedslot and element radiator adjustable for wide admittance characteristic.This invention accomplishes these objectives and offers advantageswhich, it is believed, constitute a significant contribution in waveguide techniques.

For a better understanding of the present invention, reference is madeto the following description of the appended drawings, in which:

FIG. 1 is a perspective view of the combination of a rectangular slottedwave guide and a hairpin-type coupler in accordance with the invention;

FIG. 2 is a fragmentary sectional view taken along line 22 of FIG. 1 andlooking in the direction of the arrows;

FIG. 3 is a perspective view of a modified embodiment of a slottedrectangular wave guide and trombone-type coupler in accordance with theinvention which is adjustable both as to penetration and angularrelation to the slot; and

FIG. 4 is a sectional View through the collet and seal plate utilized inpositioning the coupling element.

While the invention is simple in its mechanical presenta- United StatesPatent "ice tion, the theoretical considerations involved are complex.The Wave guide 10 is a conventional rectangular wave guide such as thetype RG49/U, operating in the TE mode. The significance of thisdesignation is that the electrical field of the guide is transverse tothe longitudinal axis of the guide and has no component in the directionof such axis. This mode is often referred to as the dominant mode of arectangular wave guide. The electrical field extends between the twoparallel walls which are most closely spaced-i.e., between the top wall11 and the bottom wall. Now, assume that .a slot 12 is formed in sidewall 13 and that the central axis of this slot extends in the verticaldirection-4e, parallel to the electrical field. A wave guide slotted inthis manner will not radiate any substantial amount of energy. Verticalslot 12 produces negligible magnetic coupling between the wave guide andouter space, because the slot is transverse to the magnetic flux anddoes not substantially interfere with the flow of currents in the guidewall. A vertical sloti.e., a slot along the short side dimension-doesnot substantially electrically couple the wave guide to-outer space,because no electrical field terminates on side Wall 13.

The theoretical factors here involved are well expressed in Electronicand Radio Engineering, Terman, pp. 128- 135, particularly pp. 133 and134, McGraw-Hill Book Company, New York, 1955.

As indicated in the Terman text just referred to, and by numerous otherauthorities such as Antennas, Kraus, page 356, McGraw-Hill Book Company,New York, 1950, it was classically taught that slots of this charactershould be cut in inclined fashion in order to make them radiate. WhileAirborne Radar, Povejsil, Raven, and Waterman, pages 526, D. VanNostrand Company, Inc., New York, 1961, points out the advantages ofside wall slots, this authority again shows them tilted. See alsoPrinciples and Practice of Radar, Penrose and Boulding, page 412, D. VanNostrand Company, Inc., London, 1949. Various workers in the artrecognized this characteristic of shortside-slotted rectangular waveguides, operating in the dominant mode, and made efforts to solve theproblem. U.S. patent to Shanks et 221., 3,004,259, is an example. Shankset al. provide ferric stubs which distort the normal magnetic fieldwithin the guide. Shanks et al. do not disclose any practical means forindividually adjusting these stubs. Now the combination in accordancewith the present invention provides inductive coupling so that magneticphase sensitivity is very small. By contrast to Shanks et al., anymagnetic field distortion in the combination of the present invention isheld to a minimum. Additionally, the present invention provides areadily adjustable combination.

In accordance with the invention, the slotted wave guide '10 is causedto radiate by the provision of a hairpin loop surface conductor 14, thebight 15 of which is inclined at an angle to the slot, and the feet 16and 17 of which are transverse to the side wall 13. The hairpin isinserted into the wave guide, and the feet slide tightly into suitablyformed apertures 18 and 19 in the Wave guide side wall 13, intrombone-like fashion.

By the provision of simple means for adjusting the coupling andradiation properties of a slotted wave guide, the present inventionmaterially enhances the field of usage of such wave guides in microwavetransmission and reception.

The depth of insertion of the loop 14 in the wave guide determines theadmittance or coupling characteristic with reference to external loads.7

Magnetic fields within the guide induce voltages in the loop 14 andcause the wave guide slot to radiate. The degree of coupling between thewave guide and outer space-i.e., the radiation fieldis varied by'controlling the penetration of the loop orthemechanical dimensions 7 ofthe loop. In practice, generally only one adjustment is made, and theloop may be secured in place by soldering the feet to the waveguide atthe apertures; Additionally, the; admittance may, be controlled byvarying the angularity (here shown as 45 degrees) of the'l-oop'with respect to the slot. Such a variation may be accomplished a by providingadditional pairs of apertures in the wave guide at different angularrelationships with respect to the slot, selectmg the desired pair ofapertures, and then filling in those unused, as with solder.

The embodiment of FIGS. 1 and 2 has been reducedto from opposite sidesof the slot when the coupling is to be reversed.

In addition to the screws 26 and 27, the plate, is fastened to the sidewall waveguide byan additional screw practice, and measurements made ata frequency of 5400 megacycles. parameters were as follows:

Width of slot 0.11 inch. Distance between slot and closed end of thewave guide f length. Angle of (i,e.-, angle between the central axis, ofthe slot and an imaginary line between the two feet ofthe hairpin) 45degr'ees.

Penetration of loop into wave guide From 17 to 31 7 millimeters.

Nature of hairpin M inch wire.

Distance between the two hairpin feet 0.3 inch.

The. advantages of a radiator invention are:

(1) Adjustable energy-coupling over a wide range;'

in accordance with the arrays are employed;

In the successfullytested embodiment, the

, a (2) Reduction of cross-polarization when Wave guide 1 32. The sidesof the arcuate slot 28 are wedge-shaped, as shown at 33 and 34, so thatas the plate 23 is securely fastened in place, the Wedge surfaces 33 and34 press the I fingers 30 of a collet 29 against'the portion 17 of thehairpin element, maintaining it in the desired position of adjustment,so far as penetration of the wave guide of the coupling element isconcerned. 7

The large skirt 35 on the upper side of the collet serves asa dust coverand weather seal for the, wave guide if Quarter wave I a In FIG. 4 theto'p'of portion (3) Slots in the wave guide elements may be milledw-itha single setting of the milling machine and without greatprecision, when a multi-slot array is fabricated;

(4) This radiator is conveniently, mechanicallyadjustable in theoperating location;

(5) This radiator may beemployed when the wave guide is excited in anyof the TE modes, and its;utility i-s not limited to the dominant mode.

In FIGS.) 3 and 4 there is shown an adjustable version of the invention.The reference numerals 10311, and 13' designate elements which are sosubstantially identical necessary. The collet makes a tight connectionof short electrical length immediately 'at the point where the hairpinemerges from the wave guide wall, since the colletis pressed intoboththe hairpin portion 17 and the wave guide Wall to obtain the wedgeaction.- Thus, good electrical contact and extremely low inductance areassured. 117 is broken away for clarity in illustration, j

While there have been shown and described what. are at'pre'se'ntcons'ideredto be the preferred embodiments of the invention,it will beunderstood by those skilled in the 3 art that various modifications andchanges may be made therein without departingifrom the' true scopeof'the invention as defined in'the appended claims, as by operating inother TE'modes, for example.

I claim; e V 1. The combination of a rectangular wave guide operating inaTE mode and formed with a normally substantially non-radiating slotextending parallel to the'electrical fieldand ac'ro'ssthe short side ofthe guide, and a hairpin-,

shaped substantially inductive coupling element mechanically positionedin the guide obl-iquelywith respect to the magnetic field behind theslot'to bridge the slot andto providea loop linked by the magneticfield, said coupling element-being formed with feet and said, guidehaving apertures adjustably receiving said-feet in; trombone tocorresponding elements in, FIGS. 1 and 2 as not to re- V quire'fu-rtherand repetitious description. Element 14 of FIG. 3 is identical to theelement 14 of FIG.'1." In the embodiment of FIGS..3 and 4, the shortside 13' of the wave guide is provided with symmetrically arrangedopposed arcuate slots 21 and 22; one on each side of the radiating slot12. Portion 17 of the trombone element 14 projects through the slot 22.and portion l6 through the slot 21. It will be observed th=atthisarrangementpermits the angular relationship of the plane of the tromboneelement-to a central plane passed through the slot 12, to be adjusted asdesired. After such adjustment is made, 'the' andpositioning means foradjusting the angular posidesired position of the coupling element ismaintained or secured by a pair of pinch and s'ealplates. such 23,

one associated'withportion 17 and one associated with a portion lfi. .1The plates are alike so that thedesc ription will be cohfined to plate23, it being shown as removed troni the wave guide for purposes ofclarity in description; The plate issecured in aperturesi24 and-'25 inthe'wave guide by screws 26 and 27, it being understood that thefashion. p I e a e 2. The combination ofa rectangular wave guideoperatingin aTE mode and formed with a" normally substantiallynon-radiating slot extendingparallelt o the electrical field and acrossthe short side of the guide, a hairpin-shaped substantially inductivecoupling ele- ;ment mechanically positioned in the guide obliquely Iwith respect to the'm'ag'netfield behind the slot to bridge the slot andto provide a loop linked by the magnetic "field, said coupling elementbeing formed with feet and said-guide'having curved slots for receivinglsaid feet', I

tion of said coupling element. 3. The combinationinaccordancelwith'claim 2' in .which the positioning means comprises apair of clamp plates having curved slotsinjregistrywith thefirst-mentioned curved slots, and; further having collets through whichthe feet of the coupling element project.

screws are loosened'when theadjustment of the element I 14 is being madeand then tightened to secure that element in the desired adjustment.Portion 17 of that element projects not only through arcuate slot 22'but also through a a slot 28 in plate 23 of approximately half thearcuate I length of slot 22. Thisarrangement permits'portion 17,

for example, to be varied in position along the slots 22 and 28.

'It is reiterated that the semi-circular slots 21 and-22 of the slot.such rotation adjusts the coupling of the I IZ efei-ence'sCitedbYExaminer" 7 HER MAN KARl. SAALBACH, Primary Examiner.

ELIIQLIBERMAN, Examiner.

1. THE COMBINATION OF A RECTANGULAR WAVE GUIDE OPERATING IN A TE MODEAND FORMED WITH A NORMALLY SUBSTANTIALLY NON-RADIATING SLOT EXTENDINGPARALLEL TO THE ELECTRICAL FIELD AND ACROSS THE SHORT SIDE OF THE GUIDE,AND A HAIRPINSHAPED SUBSTANTIALLY INDUCTIVE COUPLING ELEMENTMECHANICALLY POSITIONED IN THE GUIDE OBLIQUELY WITH RESPECT TO THEMAGNETIC FIELD BEHIND THE SLOT TO BRIDGE THE SLOT AND TO PROVIDE A LOOPLINKED BY THE MAGNETIC FIELD, SAID COUPLING ELEMENT BEING FORMED WITHFEET AND SAID GUIDE HAVING